Desulfurization and conversion of a naphtha



Feb. 2l, 1950 E. T. LAYNG ETAL DESULFURIZATION AND CONVERSION OF A NAPHTHA C5 Sheets-Sheet 1 Filed Oct. l5, 1945 INVENToRS Eo w//v 7.- LA YN@ Feb. 21, 1950 E. T. LAYNG' ETAI.

DESULF'URIZATION AND CONVERSION 0F A NAPHTHA 3 Sheets-Sheet 2 Filed Oct. 15, 1945 ED W//V TLA Y/VG Feb. 2l, 1950 E. r. LAYNG ErAL 2,498,559

DESULF'URIZATION AND CONVERSION OF A NAPHTHA Filed Oct. 15, 1945 I5 Sheets-Sheet 3 L L J II? Patented Feb. 21, 1950 DESUL'FURIZATION AND CONVERSION OF A NAPl-ITHA Edwin T. Layng, New York, N. Y., and Louis C.

Rubin, West Caldwell, N. J., assignors to The M. W. Kellogg Company, Jersey City, N. J., a

corporation of Delaware Application October 15, 1945, Serial No. .622,364

' (Cl. 19o- 28) 2 Claims.

The present invention relates to an improved process for the removal of sulfur or sulfur-containing compounds, from hydrocarbon mixtures. More particularly, the invention pertains to a process for removing sulfur and increasing the aromatic content of naphthas, or similar hydrocarbon mixtures, boiling within the motor fuel boiling range and contaminated with sulfur in amount sumcient to render them unsuitable for use for various purposes, such as a high quality motor fuel.

The organic sulfur compounds occurring in naphthas are, in the order of their thermal stability and relative ease of removal from the naphtha: hydrogen sulfide, mercaptans, disuldes, suldes, thiophanes, and thiophenes. Several of the first ve of the above six compounds usually are present in virgin naphthas, depending on its origin, while all six are usually present in cracked naphthas. Thiophene apparently is rarely found in straight run naphthas but frequently makes up more than 50% of the total sulfur of cracked naphthas. The effect of thermal treatment upon a virgin naphtha is to shift the sulfur from the easily removable types of compounds toward the most diilicultly removable types. Thiophene and its homologs exhibit a chemical inertness and thermal stability that is almost equivalent to that of benzene.

The removal of sulfur from cracked naphtha, accordingly, is a problem attended by most serious technical diculties, and one of the outstanding advantages of the present process resides in its applicability to such stocks as well as more readily desulfurizable stocks such as virgin naphtha. A further object and advantage of the invention is the provision of a process whereby substantial enhancement of the aromatic content and anti-knock quality of the naphtha. is effected simultaneously with the desulfurization. A further feature of the process resides in the maintenance of the mass velocity of the hydrocarbon feed in excess of 5 milligrams per square centimeter per second.

In Acertain of its preferred aspects, the present invention may be regarded as a modification of, and an improvement upon, the dehydroaromatization process constituting the subject matter of our application, Serial No. 294,784, filed September 13, 1939,now U. S. Patent 2,320,147. In accordance with the latter process, a naphtha fraction is catalytically converted by a dehydroaromatization reaction to a motor fuel of high aromatic content and increased octane number. In the practice of that process the naphtha undergoing treatment is mixed with hydrogen, and the mixture contacted with a dehydrogenating and cyclicizing catalyst such as molybdenum oxide supported on activated alumina, at an elevated temperature and under reaction conditions such that the naphtha is converted to a highly aromatic fuel of enhanced anti-knock value, accompanied by a net production of hydrogen. The process is preferably practiced under critically defined conditions with respect to operating variables such as temperature, space velocity, quantity of hydrogen added, and the like. Our prior process is applicable to the treatment of naphtha stocks or similar hydrocarbon mixtures generally, including both straight run virgin naphthaand cracked naphtha. In the case of cracked stocks, the process contemplates as a preferred procedure the maintenance of a relatively low maximum pressure not over about 250 pounds per square inch and preferably in the range of about 30-200 pounds per square inch in contrast to a range of about 30 to 450 pounds per square inch for virgin naphtha stocks;

The procedure followed in the practice of the present invention, its various salient features and advantages, may be most readily understood by considering its application to the processing of various charging stocks as described hereinafter in connection with the appended drawings which illustrate a suitable arrangement of apparatus and process-flow for use in the practice of the invention.

Referring to the drawing of Figure 1, the lnvention may be suitably practiced in a continuous operation by using a plurality of catalytic reactors numbered l to 6 and arranged in a parallel relationship as shown and manifolded with fluid inlets and outlets so that each reactor may be alternatively placed on the conversion or onstream cycle by flowing reactants thereto, and then switched on to the regeneration cycle wherein the catalyst is regenerated by flowing a regeneration fluid therethrough. The number and size of reactors employed may be varied, dependent upon lparticular conditions such as the capacity required. In the embodiment illustrated. six are employed, two of these numbers 2 and 5 at the period illustrated being on the on-stream cycle, and the other four being in various stages of the regeneration cycle.

In place of a static or stationary bed type of catalytic reactor such as shown in the drawing, a moving bed type of reactor may be employed as shown in Figures 2-4 inclusive. In the latter, continuous operation is obtained by passing the reactants continuously in contact with a mass or bed of the catalyst which may be granular, pelleted or powdered in a reactor vessel provided with gas-tight valve means for feeding fresh or regenerated catalyst into the upper end of the reactor and withdrawing spent catalyst from the lower end. Suitable piping connections are provided in the shell of the reactor, below and above the valve means, for introducing and withdrawing the reaction vapors. The reactants in this arrangement may be passed in a direction either concurrent or countercurrent to the direction of the movement of the catalyst although we prefer countercurrent. With this type of reactor the spent catalyst is not regenerated in situ, butin a separate unit under any desired conditions. Also, in this case there is no on-stream lthe principle is illustrated in the above-mentioned application The naphtha charging stock is introduced through line 6' into a heating coil 1 in furnace 8 wherein it is vaporized and heated to an elevated temperature suitable for theconversion. Hydrogen, or a gas containing hydrogen, such as a recycle gas separated from the conversion products, is introduced through line 9 into the heating coil I in furnace 8 and likewise is heated to a temperature suitable for the conversion. The naphtha and hydrogen are withdrawn from the furnace through 'lines I2 and Il, respectively, and introduced into transfer line i3 leading to the catalytic reactors I-S.k From transfer line I3 the mixture of hydrogen and naphtha vapor is introduced through open valve Il of the reactors on-stream numbers 2 and 5 and through themain inlet line I of each of these reactors into the catalytic mass therein. The catalytic mass prior to the introduction of the reaction mixture of hydrogen and naphtha is preferably brought up to the desired reaction pressure with recycle gas, and is also preheated to a temperature approximating the conversion temperature. During the passage of the reactants in contact with the catalyst the desired conversion reaction takes place as described in detail hereinafter.

The vaporous conversion products are withdrawn from reactors 2 andi through main outof 110 F., andan end point of 400 a sulfur content of 0.7% and an octane number of 62. The cracked naphtha component had a gravity of 50.0 A. P. I., an initial boiling point of 110 F. and an end point of 410 F., a sulfur content of 2.0% and an octane number of 69.

let line i6 and open valve I1 and pass to transa mer boiling above the gasoline boiling range, and

a lgaseous fraction containing a mixture of hydrogen and normally gaseous hydrocarbons having 1 to 3 carbon atoms in the molecule. A portion of this gaseous fraction constitutes the recycle gas introduced through line 9.

In accordance with one example, the process was applied to the desulfurization and reforming of a naphtha. stock of California origin-and representative of the type of high sulfur stocks which are especially diiiicult to process satisfactorily. In this run a blend of approximately cracked and 30% virgin California naphtha was employed. The blend had a gravity of 50.9 A. P. I., an initial boiling point of 110 F., and an end point of 410 F., A. S. T. M. distillation, a sulfur content of 1.75%, and an octane number of 67 (C. F. R. M.) The virgin naphtha component of the blend had a gravity of 54.0 A. P. I., an initial boiling point This naphtha blend was contacted with a dehydrogenating and decyclicizing catalyst comprising 12% molybdenum oxide supported on activated alumina, and processed in a static bed type of equipment shown in the drawing pursuant to the procedure described above, and under operating conditions maintained as indicated below:

Example I Operating Conditions Value Time Factor, F 1.60 hrs. Space Velocity 0.6. Average Reaction Temperature (T) 970 F. Severity Factor (S) 902. Pressure within Rea 100 lbs/sq.

ctor in. Recycle Gas (40% Hydrogen) (Rate 6000 cu.tt./bbl. naphtha added). charged. Hydrogen added (Mol ratio of hydro- 2.8.

gen to mol oi naphtha charged). Time On-stream 2 hrs. Mass velocity'. 38 mgJcm/sec.

Per cent Gasoline 78.5 Liquid polymer 3.5 Dry Gas 10.8 Carbon (deposit on the catalyst) 4.5 Sulfur (deposit on the catalyst) 1.7

The above yields are on the basis of complete recovery of the C4 hydrocarbons with the gasoline fraction. The gasoline produced had a gravity of 51 A. P. I., an initial boiling point of 92 and an endv point of 400, a sulfur content less than 0.1% and an octane number of 80.

The dry gas produced consisted of 40% hydrogen, 35% methane, 15% of C2 hydrocarbons and 10% of C3 hydrocarbons.

In this example, substantially complete desulfurization of the feed stock was effected, both the liquid and gaseous products being substantially sulfur. free, and in addition a high yield of 78.5% of asulfur-free motor fuel was produced having an octane number of compared with an octane number of only 67 for the feed stock.

The improvement in anti-knock characteristics or octane number of the naphtha subjected to treatment in accordance with the invention, is attributed largely to the dehydrogenation and cyclization of aliphatic hydrocarbons contained in the naphtha feed to aromatic compounds. The desulfurization is attributed to the retention of the sulfur content of the charge on the catalyst as molybdenum sulde. It has been observed that substantially no sulfur appears in either of the gaseous or liquid products until a considerable proportion of the molybdenum oxide content of the catalyst has been converted to molybdenum mono-sulfide. After this point has been reached the sulfur content of both the gaseous and liquid products tends to rise sharply, coke production increases, and the hydrogen concentration in the circulated recycle gas falls oil.

An important advantage of the procedure illustrated by the above example is that both gaseous and liquid products are substantially sulfur free, and the sulfur is left in a chemically combined condition on the catalyst. This type of desulfurization is to be distinguished from the type wherein the sulfur is converted to hydrogen sulde and is removed as such along with the other product gases. In the latter type of operation. a further treatment of the product gas is usually necessary for the removal of its hydrogen sulfide content to adapt it for use for various purposes, such as recycling in the system. For the foregoing reasons in the practice of the invention, we prefer to employ a catalyst comprising molybdenum oxide catalyst or other dehydrogenating and cyclicizing catalysts which have a strong ailinity for sulfur and are capable of combining therewith under the conditions of the reaction to produce the corresponding metal sulfide.

It is to be noted that in the above example the ori-stream cycle was limited to two hours. This period is substantially shorter than the ori-stream period which could be used with satisfactory results in the reforming to the same extent of a charging stock consisting of naphtha of vsimilar composition to that utilized in the example but differing therefrom in being substantially free of sulfur. The preferred length of the on-stream cycle may be xed for any given set of conditions by determination after the system is onstream the point at which the sulfur content of the gas and liquid products tends to rise sharply. In the example given this effect was observed after an on-stream period of about two hours.

The following example exemplifies the practice of the invention as applied to the desulfurization and reforming of a low octane, high sulfur virgin naphtha stock employing a dehydrogenating and cyclicizing catalyst consisting of 6% molybdenum oxide on activated alumina and also employing a static bed type of reaction procedure as described above. The inspection of the feed stock, operating conditions maintained, and the yield of products are shown in tabulated form in the following:

Example II (a) Inspection of feed stock:

Gravity, A. P. I 50.0 A. S. T. M. distillation:

I. B. P., F 244 E. P 408 Sulfur, weight per cent 0.283 Octane number, C. F. R. M 43.4

(b) Operating conditions:

Space velocity, vol. naphtha/hr./vol. cat 0.50 Average reaction temperature, F 945 Severity factor (S) 975 Pressure, lbs/sq. in 200 Recycle gas, recirculating rate, cu.ft./bbl. naphtha 2,750 Mols H2 in circulating gas/mol. naphtha 2.0 On-stream cycle, hrs 6 Mass velocity mg./cm.2/sec 19 In the above example constituting a laboratory pilot plant run, the reactor consisted of a vertically disposed pipe 7 feet in length and inside diameter of 2 inches in which the depth ofthe catalyst bed was six feet, thereby resulting under the other prescribed conditions in a mass velocity of 19 milligrams per square centimeter per second.

' (c) Yields of products as per cent of naphtha charged:

Weight per cent gasoline C4 recovery) 83.9 Weight per cent liquid polymer 2.7 Weight per cent gas (C4 free) 11.4 Weight per cent coke 1.7 Weight percent sulfur (deposit on catalyst) 0.283

(d) Product inspections:

Gasoline (100% C4 recovery):

Gravity, A. P. I 46.4 Octane number 83.0

Sulfur Free Dry gas, composition:

Vol. per cent Hz 59.3

Vol. per cent Ci--Cz 40.7

(a) Operating conditions:

Space velocity, vol. naphtha/hr./vol.cat 0.4 Pressure, lbs./sq.in 100 Average reaction temperature, "F 970 Recycle gas recirculating rate, cu.ft./bbl.

naphtha 5,000 Catalyst holding time, hrs 1.6 Mass velocity mg./cm.2/sec 17 In the above example the reactor employed was that illustrated in Figure 2 through which the catalyst was moved continually, the reactor being a pipe 7 feet long and two inches inside diameter, the catalyst bed being maintained at a height of 61/2 feet therein as indicated on Figure 2, with a resultant mass velocity of the hydrocarbon feed under the prescribed conditions of 17 milligrams per square centimeter per second.

(b) Yield of products as per cent of naphtha charged:

Volume per cent gasoline (100% C4 recovery); 75.8 Weight percent gas 10.8 Weight per cent coke 6.5 Weight per cent sulfur (removed) 2.1

(c) lInspection of products:

Gasoline (100% C4 recovery) Octane number (C. F. R. M.) 81.9 Sulfur, weight per cent 0.14

In Example IV, the catalyst was molybdenum oxide on alumina and the charging stock was an East Texas heavy naphtha having an A. P. I. gravity of 50.3, containing approximately 14% aromatics, 33% naphthenes and no olens, the remainder being largely paraiin hydrocarbons. This naphtha had an initial boiling point of 248 F., a 50% boiling point of 310 F. and an end point of 396 F. The original octane number measured by the Cooperative Fuel Research Motor Method, as were all the octane numbers mentioned herein, was 42.3.

Example IV Run number 902 Severity factor (S) 1,031 Temperature (T), "F 971 Time factor (F), hrs 4 Pressure, lbs/sq. in. 100 Mol ratio, Hz/charge (M) 8 Catalyst holding time, hrs 10 Mass velocity mg./cm.2/sec 11 Product characteristics:

4Octane number 87.9 Yield. per cent '78.2 Gravity, A. P. I 39.7 Aromatics, per cent 62.9 Oleiins, per cent 10.1 Coke, per cent 1.0 Difference between 50% distillation points of charging stock and product, "F 40 Hydrogen produced, mols Hz/ mol charge 0.91

In Example IV, the catalyst was moved continually through the reactor, the latter being the same as that employed in Example III and the bed therein being maintained at substantially the same height, as in Example III, providing a mass velocity of 11 milligrams per square centimeter per second.

The preceding Iexamples illustrate the practice of the invention under sufliciently varied conditions to illustrate its underlying principles. It will be apparent to those skilled in the art that the process may be. practiced under a wide range of conditions with respect to such factors as a charging stock, catalyst, and operating conditions employed, and that lfor any particular charging stock and catalyst the most suitable operating conditions for securing a high degree of octane improvement and sulfur removal are preferably determined by a few experimental runs. In the following, the general principles are given which guide the selection of suitable conditions for the practice of the invention.

Either high sulfur virgin, or high sulfur cracked naphthas, or blends thereof, containing a substantial amount of aliphatic hydrocarbons boiling within the motor fuel range and characterized by their low octane number may be treated pursuant to the invention. The invention is especially well exemplified in its application to cracked naphtha s-tocks because of the relatively great difficulty encountered in eliminating sulfur and improving octane rating of such stocks by any methods heretofore available.

The catalysts used in our process are those capable of effecting the dehydrogenation and cyclization of aliphatic compounds to aromatic compounds of which there are a number known in the art. Of these catalysts those comprising molybdenum oxide are especially advantageous and are preferred. Of those catalysts which differ from molybdenum catalysts in that the sulfur is separated in the form of hydrogen sulde rather than` in combined form on the catalyst, we prefer those comprising chromium oxide. Both catalysts may be used supported on any suitable carrier of which an activated alumina is the preferred support. Although molybdenum and chromium catalysts are regarded as the preferred catalysts, we may employ the oxides of suldes of other metals of the left-hand column of group VI of the periodic table and other metallic compounds, particularly oxides of the metals of the left-hand column of groups IV and V of the vperiodic table, such as titanium, cerium, thorium and vanadium. Moreover, while these catalytic oxides can be used alone or on various supports we find it highly preferable to utilize them supported on alumina, particularly activated alumina.

The following is given as illustrative of a suitable procedure for use in the preparation of the catalyst, the particular example being directed to the preparation of a molybdenum oxide catalyst on activated alumina:

Dissolve kilograms of ammonium para molybdate in sufficient distilled water to yield 1500 liters of solution. Place 1500 kilograms of granular activated alumina in an apparatus which can be evacuated and add the molybdate solution. Agitate the mixture and then apply a vacuum pump and reduce the pressure to 30-40 millimeters of mercury. Then allow the pressure to rise to atmospheric. Lower the pressure a second time to the same level and then allow it to rise again to atmospheric pressure. Repeat this procedure a third time and then drain the remaining liquid from the impregnated alumina. Air-dry the latter on screens or other suitable containers using layers of about one inch in depth. At the end of this time place the dried material in a furnace in a suitable container and heat it at a temperature of 1200 F. for one hour. Cool to atmospheric temperature and storein closed containers until ready for use.

Very important advantages are obtained by carrying out the reaction in the presence of added hydrogen and we greatly prefer to employ this feature in the practice of the invention. The use of hydrogen in suitable amounts cuts down the formation of coke very markedly and thereby increases the length of runs to the point where regeneration is not necessary at the frequent intervals that would otherwise be essential. In general, we prefer to add hydrogen in the range of about 0.5 to 8 mois of hydrogen per mol of naphtha charged. The quantity of hydrogen added is dependent upon the degree of severity and in general higher proportions of hydrogen are desirable with higher degrees of severity.

Maintenance of the reaction zone under a suitable degree of super-atmospheric pressure has .been foundto be important in securing full advantage of carrying out the reaction in the presence of added hydrogen. The use of moderate pressures markedly decreases the amount of coke deposition and increases the length of on-stream cycle or catalyst holding time. In addition the use lof such pressures increases the octane number of the product. We prefer to use pressures within the range of about 30 pounds per sq. in. to 450 pounds, or preferably within the range of about 50 lbs. to 375 lbs. When cracked naphthas, or stocks made up vlargely of cracked naphtha, such as stocks given above are charged, we prefer pressures of about 30 to 150 lbs. per sq. in. and in general, pressures not in excess of about 250 lbs. per sq. in. since higher pressures have the tendency the result in the net consumption of hydrogen. In general, We avoid the use of the high pressures and high hydrogen concentrations which result in hydrogenation and net consiunption of hydrogen.

One of the important operating variables in the process is the space velocity, or its reciprocal or time factor, which may be defined as the length of time in hours required to put through the i catalyst a volume of feed (measured as liquid) equal to the volume of the catalyst chamber, the l volume of the catalyst chamber being the overall volume oi that portion of the chamber which is filled with the catalyst. In other words, time factor isthe volume of catalyst space divided by the feed rate in volumes per hour. We have found that the time factor should be between 0.1 and 25 and preferably between 0.2 and 20 hours. Time factor or its reciprocal, the space velocity, is the important factor. rather than contact time.

Not only is time factor important but temperature is likewise important and should be in the range of about 850 to 1050 F., and preferably in the range of about 900 to 1000 F. If the temperature is lower than the minimum specified the reaction is unsatisfactorily slow and does not produce the desired high yield of aromatic hydrocarbons from aliphatic hydrocarbons. With cracked stocks, temperatures in the upper portion of the specified range are preferred because of the tendency of excessively low temperatures to result in hydrogen consumption in place of hydrogen production.

When we speak of temperature in this specification and in the appended claims we refer to the temperature as measured in the'catalyst bed unless some other meaning is indicated. The catalyst bed temperature to which reference is made is the weighted average temperature calv culated from temperature measurements made at a plurality of representative points in the catalyst bed.

The temperature maintained in the reaction and the rate of flow of the naphtha over the catalyst are operating conditions which are in a dependent relationship with reference to the results produced. For example, within limits an increase in the time factor will give the same eect as a certain reduction in the temperature. We refer to this relationship as severity factor and in the conversion of virgin naphtha stocks the severity may be defined as,

where T is the temperature in degrees Fahrenheit and F is the time factor in hours. This equation deflnes severity in such terms that with a given virgin naphtha charging stock and other process conditions being held constant, all runs using a given severity factor will give approximately the same octane number product. Since the high octane number of the product is due largely to its high content of aromatic compounds, it may be said that the content of aromatics is a function of severity factor and a certain minimum severity factor is preserved in order to secure the beneficial increase in octane number. With extremely active catalysts this minimum severity factor can be about 925 but in order to obtain the best results the minimum severity factor should be 950 or 975. At the same time if either the time factor or the temperature is too high, unsatisfactory results are obtained and there is thus a critical maximum as well as a critical minimum on severity and this maximum is 1100 or, for best results, 1075.

As previously noted the process mayv be most advantageously practiced by utilizing higher proportions of hydrogen with higher degrees of severity. In other Words, the maximum mol ratio (or partial pressure) of hydrogen to charge is a function of the severity factor used and higher severity factors are most advantageously employed with high concentrations of hydrogen. It has been ascertained that the range of optimum 10 mol ratio of hydrogen for use with a given severity factor may be expressed mathematically by the following equations:

Optionally, the denominator in the first of the above two equations can be 100 instead of 125. 'I'he preferred moi ratio of added hydrogen lies between the limits M and M1 and between the preferred mol ratio limits of 0.5 and 8.

While the limits above specified of severity factor and optimum mol ratio of hydrogen do not apply to the treatment of cracked naphtha stocks as closely as in the case of virgin stocks, the same general principle does apply and in general we prefer to operate in the case of cracked naphtha stocks in about the same ranges of severity factor and optimum hydrogen addition as specified for virgin naphtha stocks.

After the on-stream period the catalytic mass may suitably be regenerated by contacting it at a suitable temperature with an oxygen-containing gas for removing the de-activating deposits by combustion. During the regeneration, the carbonaceous material is eliminated as carbon dioxide, and the sulfide of the catalytic metal is converted into the corresponding oxide and sulfur dioxide. The complete regeneration procedure will usually involve several steps including a purging treatment to remove residual hydrocarbons prior to the combustion reaction and a purging treatment after this reaction to remove residual oxygen-containing gas, a reheating treatment, and adjustment of pressure between the various steps.

Tabulated below are the several steps included in atypical complete processing period covering a period of 6 hours including the reaction and regeneration steps and the elapsed time for the individual steps:

Time

Operation Steps Mins. Secs.

Depressuring Purge before Reaction Valve Operation Total gewesen The hydrocarbon purge after reaction may be effected by introducing a purging gas, suitably a portion of the recycle gas similar to that introduced through line 9, by opening valve 2| in line 20 and reactor valves 22 and I4, all reactor valves being closed except valves 22 and I4. The purged material is thus returned to a reactor on the reaction cycle through line I3. Repressuring may then be effected by closing valve I4 and continuing the introduction of gas from line 20 for a short period.

The inert purge may suitably be effected by opening valves 23 and 24, the remaining reactor valves being closed, and permitting flue gas from a reactor undergoing combustion to ow from line 25 through open valve 23 into the reactor, and out of the reactor through flue gas outlet line 26.

In the combustion step, a mixture of air and l 1 flue gas suitably at a temperature slightly above the ignition temperature of the deposit and at a pressure, for example about 175 lbs. gauge, somewhat higher than that employed in the conversion step is introduced into the reactor from lines 21 and 2s, respectively, bfyeaening valves 29 and 30. The hot combustion products are withdrawn from the reactor through open valve 23 and exit through the flue gas outlet line 25, all reactor valves other than those mentioned being closed.

A reheating step is usually advisable since the catalytic mass after combustion will be cooled down to the temperature of the entering mixture of air and iiue gas which preferably is at a temperature approximating the ignition temperature of the deposit, that is a temperature of about 700 F. In the reheating step, hot iiue gas is introduced through line 25 from a reactor undergoing combustion by opening valves 23Y and 24, thereby circulating hot flue gas through the reactor from line 25 and out through lines 2G until the catalytic mass is brought up to a temperature suitable for conversion. The pressure in the reactor may then be decreased by suitable operation of valve 24 to a pressure approximating that desired for conversion.

The purging treatment before reaction is effected by opening valves 22, 24 and 2|, respectively, and circulating recycle gas from line 20 through the reactor and out of the system through ilue gas outlet line 26. If desired, the catalyst may be further preconditioned by treatment with hydrogen as described in our application Serial N0. 294,785, led September 13, 1939, noW U. S. Patent 2,320,147.

While out invention can, as has been described, be used in connection with a stationary catalyst bed or a plurality of stationary catalyst beds, we nd that particularly good results can be obtained by the use of a moving catalyst bed and one embodiment of this type of invention is shown in Figures 2-4 inclusive.

Turning now to Figure 2 in more detail, a feed, which can have the characteristics previously described, is pumped from feed stock tank by means of pump |02 through coil |03 in heater |04. Simultaneously hydrogen from any suitable source, including recycle hydrogen, if desired, is passed through the same heating coil although separate heating coils can be used. As shown, hydrogen from tank |05 passes through pressure reducing valve |06 and meter |01 and thence through throttle valve |08 into coil |03. From the heater the hot mixed hydrogen and feed stock pass through line |09 to the top of a reaction chamber ||0 as will be described in` more detail in connection with Figure 3. This reaction chamber consisted, in the laboratory model of a 7 foot length of 2 inch extra heavy tubing surrounded by an electrically heated lead bath to supply the heat of reaction but for plant use a jacket I heated by ue gas introduced through valved line ||2 and withdrawn through valved line 3 is preferred.

The granular catalyst of the type previously described is added by means of inlet ||4 passing through valves ||5 and H6 separated by an injection line |1 for nitrogen, ue gas, or steam to act as a gas lock. The catalyst passes downward through the reaction chamber ||0 and the hot charging stock and hydrogen pass concurrently therewith although countercurrent flow can likewise be used. The catalyst is supported at the bottom on a rotary feeder ||8 which permits it to pass slowly downward through the reaction chamber, thence throughvalves ||9 and |20 separated by a gas lock |2| with intermediate nitrogen or other inert gas injection and thence to a catalyst revivication chamber which is not shown. In this revivication chamber the catalyst is, of course, treated with a hot oxidizing gas to burn off the coke and other carbonaceous material, care being taken to control the temperature so that the catalyst will not be injured. The regenerated catalyst is returned to inlet ||4. Reaction products pass out from the reaction chamber in a manner which will be described in connection with Figure 4 through line |22 and thence to a trap |23, which can be packed with glass wool or the like, where any catalyst carried' with the products is deposited and can be removed periodically. The products then go to cooler |24 and high pressure separator |25. In this high pressure separator the hydrogen carrying with it some light hydrocarbon gases is separated from the aromatized naphtha. The gas passes overhead through line |26 and pressure control valve |21 and thence through line |28 to absorber |29 where it is stripped with the usual absorption medium to remove residual valuable hydrocarbons. The remaining gas rich in hydrogen is vented through valve line |30. The hydrogen thus vented is substantially in excess of the hydrogen originally introduced. Alternatively excess gas can be removedl through valved line |28a and recycled to the reaction chamber.

Turning to the liquid product from high pressure separator |25, this passes through line |3| and pressure or liquid level controlled valve |32 to a low pressure separator |33 in which some additional gas containing not only a little hydrogen and Vsome light hydrocarbons but also an appreciable amount of butane and other valuable light naphtha constituents passes out through line |34, cooler |35 and line |28 to absorber |29 where it is contacted along with the gases from high pressure separator |25 with an absorption medium introduced through line |36 by means of pump |31 and withdrawn through line |38 by means of pump |39 passing through heat exchange |40 and heater |4| to stripper |42 equipped with the usual reboiler coil |43 and dephlegmating coil |44. The lean oil from the stripper passes through heat exchanger |40 and cooler |45 back to pump |31 and absorber |29 for reuse. The stripper yields an overhead consisting largely of light ends of motor fuel and this passes through line |46 and cooler |41 back to low pressure separator |33. The final product is withdrawn through valved line |48.

Referring now to Figure 3, the granular catalyst from hopper I4 which may be made up predominantly of granules within the range from 2 mesh to 50.mesh, for instance 4 mesh passes through valve ||5 which can'be continuous or discontinuous in its operation into chamber |49 wherein inert gas is injected to prevent diffusion of naphtha vapors out of the system. Thence the catalyst passes through valve IIB, which can often be omitted or left open, into a'tapering tube |50 wherein the hot charge and hydrogen introduced through line |09 preheat the catalyst in indirect heat exchange and the hot catalyst passes into reaction chamber ||0.

The bottom of this reaction chamber is shown at the top of Figure 4. The catalyst passes by gravity iiow out of reaction chamber ||0 into a chamber 5| formed by screen |52 having a mesh smaller than the smallest catalyst grains. Catalyst ow is regulated by rotary valve ||8 which 13 is operated through shaft |53 by a variable speed motor not shown. The catalyst then passes through valve I I 9, which can in some cases be left open, into gas lock chamber `|54 and thence through continuous or intermittent valve |20 to the regeneration system.

This application is in part a continuation of application Serial No. 358,750, now abandoned, filed September 28, 1940, and in part a continuation of application Serial No. 440,762, now abandoned, i-lled April 28, 1942.

We claim:

1. A cyclic process for the conversion of a high sulfur content naphtha to a motor fuel of increased aromatic content and` anti-knoclr` quality and substantially free-trom sulfur in any form,4

which comprises passing such a hydrocarbon feed stock at a mass velocity in excess of five milligrams per square centimeter per second in the presence of added hydrogen in contacty with a catalyst comprising molybdenum oxide at a temperature between about 850 and about 1050 F., a pressure between about 30 and about 450 pounds per square inch, within a time factor range of about 0.1 to about 25, such that the naphtha feed stock is converted to one of increased aromatic content and substantially all of the sulfur is combined with the catalyst to produce an efiiuent substantially free from sulfur in any form, maintaining the quantity of hydrogen added and the pressure within limits insuicient to cause a net consumption of hydrogen, continuing contact of such a naphtha with the catalyst for a period of time not longer than that required for the sulfur content of the elliuent to rise sharply, thereafter discontinuing contact of such a naphtha and regenerating the spent catalyst by contact with an oxygen-containing gas at an elevated temperature to remove combined sulfur from said catalyst, and repeating the above cycle with said regenerated catalyst.

2. A cyclic process for the conversion of a high sulfur content cracked naphtha to a motor fuel of increased aromatic content and anti-knock 14 quality and substantially free from sulfur in any form, which comprises passing such a hydrocarbon feed stock at a mass velocity in excess of live milligrams per square centimeter per second in the presence of added hydrogen in an amount of about 0.5 to 8 mols of hydrogen per mol of naphtha charged in contact with a catalyst comprising molybdenum oxide supported on alumina at a temperature between about 900 and about 1000 F., a pressure between about 30 and about 200 pounds per square inch, within a time factor range of about 0.2 to about 20, such that the naphtha feed stock is converted to one of increased aromatic content and substantially all of the sulfur is combined with the catalyst to produce an efluent .substantially freaffrom sulfur in any form, maintaining the quantity of hydrogen added and the pressure within limits insuicient to cause a net consumption of hydrogen, continuing contact of such a naphtha with the catalyst for a period of time not longer than that required for the sulfur content of the effluent to rise sharply, thereafter discontinuing contact of such a naphtha and regenerating the spent catalyst by contact with an oxygen-containing gas at an elevated temperature 'to remove combined sulfur from said catalyst, and repeating the above cycle with said renegerated catalyst.

EDWIN T, LAYNG. LOUIS C. RUBN.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Hillman May 9, 

1. A CYCLIC PROCESS FOR THE CONVERSION OF A HIGH SULFUR CONTENT NAPHTHA TO A MOTOR FUEL OF INCREASED AROMATIC CONTENT AND ANTI-KNOCK QUALITY AND SUBSTANTIALLY FREE FROM SULFUR IN ANY FORM, WHICH COMPRISES PASSING SUCH A HYDROCARBON FEED STOCK AT A PASS VELOCITY IN EXCESS OF FIVE MILIGRAMS PER SQUARE CENTIMETER PER SECOND IN THE PRESENCE OF ADDED HYDROGEN IN CONTACT WITH A CATALYST COMPRISING MOLYBDENUM OXIDE AT A TEMPERATURE BETWEEN ABOUT 850 AND ABOUT 1050*F., A PRESSURE BETWEEN ABOUT 30 AND ABOUT 450 POUNDS PER SQUARE INCH, WITHIN A TIME FACTOR RANGE OF ABOUT 0.1 TO ABOUT 25, SUCH THAT THE NAPHTHA FEED STOCK IS CONVERTED TO ONE OF INCREASED AROMATIC CONTENT AND SUBSTANTIALLY ALL OF THE SULFUR IS COMBINED WITH THE CATALYST TO PRODUCE AN EFFLUENT SUBSTANTIALLY FREE FROM SULFUR IN ANY FORM, MAINTAINING THE QUANTITY OF HYDROGEN ADDED AND THE PRESSURE WITHIN LIMITS INSUFFICIENT TO CAUSE A NET CONSUMPTION OF HYDROGEN, CONTINUING CONTACT OF SUCH A NAPHTHA WITH THE CATALYST FOR A PERIOD OF TIME NOT LONGER THAN THAT REQUIRED FOR THE SULFUR CONTENT OF THE EFFLUENT TO RISE SHARPLY, THEREAFTER DISCONTINUING CONTACT OF SUCH A NAPHTHA AND REGENERATING THE SPENT CATALYST BY CONTACT WITH AN OXYGEN-CONTAINING GAS AT AN ELEVATED TEMPERATURE TO REMOVE COMBINED SULFUR FROM SAID CATALYST, AND REPEATING THE ABOVE CYCLE WITH SAID REGENERATED CATALYST. 